When a data signal is transmitted from one semiconductor integrated circuit (IC) device to another semiconductor IC device, the IC device receiving the data signal typically identifies the logic level or logic state (i.e., the data value) of the received signal by use of a fixed reference signal of a fixed voltage. For example, where the transmitting part of an IC device transmits a signal of the waveform shown in FIG. 1A and the receiving part of the IC device receives a signal of the waveform shown in FIG. 1B, the receiving part identifies a data value (“0” or “1”) represented by the received signal by comparing the voltage level of the received signal with a fixed reference voltage level REF.
As the transmission speed of the electrical signal increases, the difference between voltage level changes in the received electrical signal decreases. This results in a possible decrease in the difference between the voltage level of the received data signal and the voltage level of the reference signal, and makes it difficult to identify the logic state of the received signal. In addition, when an intermediate voltage level of the received signal is not identical with the voltage level of the transmitted signal due to noise or the like, there is a high possibility that the data value of the received signal is erroneously identified. The signal portions {circle around (1)}, {circle around (2)}, {circle around (3)}, and {circle around (4)} of the received signal of FIG. 1B are specific examples, each of which has a high possibility of erroneous identification.